As the friction engagement device of the automatic transmission in related arts, there has been known a friction engagement device having a frictional engagement element, a hydraulic piston and a return spring. In this friction engagement device, by exerting an engagement pressure that overcomes a biasing force of the return spring, the engagement operation of the frictional engagement element is performed, and by the biasing force of the return spring by draining the engagement pressure, the disengagement operation of the frictional engagement element is performed (See, for instance, Patent Document 1).